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Joel Topf, MD FACP @kidney_boy
, 5 tweets, 2 min read Read on Twitter
Everyone knows that potassium is an intracellular ion. And everyone knows that giving 40 mEq of KCl will raise the serum potassium by 0.4 mmol/L.

How much of that KCl infusion remains in the extracellular compartment? Not much, but more than I expected.
Let's start out by calculating the total extracellular potassium in our bodies:

70 kg * 60% water = 42 liters Total body water
one third of total body water is extracellular = 0.33*42 = 14 liters
14 * 3 mEq/L of K in our hypokalemic dude gives extracellular K of 42 mEq
Now lets give this guy 40 mEq of KCl by IV
His potassium goes up to 3.4 mEq/L as we know (…)

new extracellular K is 3.4 * 14 or 47.6 mEq of potassium
To find how much potassium remained in the extracellular compartment (and how much went into the intracellular compartment) subtract 47.6 from the original 42 to get 5.6 mEq, or 14% of the infusion.
If you don't think that's cool, maybe nephrology is not for you.
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